The purpose of this invention is to provide an all-weather, long-range control system for spinning command-guided projectiles. Such projectiles can be very low cost, since they do not require seekers or complex on-board computers for processing seeker information. Furthermore, a spinning projectile needs only a single deflection thruster to maneuver in any direction since the thruster can be fired at any appropriate roll angle. In operation, a projectile is launched and tracked during flight toward a predesignated target. When it is determined that accumulating errors will cause a miss, a single-shot thruster may be fired late in the flight to correct the trajectory errors.
Previous techniques to measure the roll angle of a projectile generally fall into one of several categories. One technique is to equip the projectile with a roll gyroscope and a data link to communicate its roll angle to the launch and flight control system. The approach is expensive since each projectile must carry an inertial navigation system, typically using gyroscopes, which must be hardened to withstand the large launch accelerations of a gun.
In another technique, the projectile is provided with a polarizing reflector for a radar or laser. The polarization angle of the received reflections indicates the roll angle, but this method suffers from an ambiguity of 180.degree. in roll. The method is unable to distinguish up from down. Thus, half the time, the projectile will be commanded to thrust in the incorrect direction.
Another technique is to provide the spinning projectile with an optical sensor to discern the difference between sky and ground. This method is not all-weather and not very accurate.
In another technique, the projectile is imaged with a camera shortly after launch to determine its roll angle and remove the 180.degree. ambiguity. Polarized reflections are then used to determine subsequent roll. This method will fail if the data stream is interrupted during flight by any obscuration such as smoke, dust etc.